(1) Field of the Invention
This invention relates to an optical disc used for recording video data, a recording apparatus, and a computer-readable recording medium recording a file management program.
(2) Description of the Prior Art
Recently, optical discs such as CD-ROMs and DVD (Digital Versatile Disc)-ROMs have been used for recording video data (also called AV data in this document) of movies or the like, as well as being used as secondary storages for computers. Currently, practical uses of DVD-RAMs are awaited because of the general expectation that DVD-RAMs will be popular as the main recording medium of the next generation.
First, conventional DVD-ROMs are explained in terms of special reproductions. The special reproductions include fast forwarding or rewinding AV data at a speed n times as high as the normal reproduction speed (hereinafter such a speed is called n-speed).
The AV data to be recorded in DVD-ROMs is compressed with a compression encoding method at a variable bit rate to increase the compression rate. The “variable bit rate” means that the amount of compressed image data per one frame is variable. As a result, the amount of compressed data is not proportionate to the reproduction period. When this happens, even if the coded AV data is read out at steady intervals, that is at every predetermined size of the coded AV data, the read-out AV data does not correspond to images to be sectioned per predetermined time period.
To relate the amount of compressed data to the reproduction period, information of each special reproduction is inserted into necessary points in the AV data in DVD-ROMs.
More specifically, the AV data is compressed in compliance with MPEG2. Through the compression, information called NV pack which is unique to DVD is added to the start of each GOP (Group of Pictures). GOPs are sections which each have a period of 0.4 to 1.0 seconds. Exceptionally, an end of a VOB (Video OBject) has a GOP of 1.2 seconds. Data included between one NV pack and the next NV pack is called VOBU (Video OBject Unit)
Each NV pack includes 2K-bytes of information used for referring to adjacent NV packs. Each NV pack also includes the data size of the first reference picture in a GOP. The information used for referring to adjacent NV packs is composed of relative addresses of NV packs of VOBUs in the forward and backward directions separated by a predetermined time period from the current VOBU, the relative addresses being obtained based on the start time code of the current VOBU. The predetermined time period may be one to 15, 20, 60, 120and 240 seconds.
Secondly, operations of special reproductions such as fast forwarding and rewinding are described. The special reproductions substantially at a steady speed are attained by reproducing only the reference pictures of VOBUs having a predetermined time interval in between, in accordance with the reproduction speed. To sequentially read out the VOBUs having a predetermined time interval in between, the information used for referring to adjacent NV packs in each NV pack is used.
A time search map is recorded in every time code that is arranged with a predetermined time interval in between from the start of the AV data. The time search map indicates an address of a piece of AV data in the VOBU corresponding to the current time code. By referring to the time search maps, reproduction apparatuses can start reproducing the AV data starting from the specified time codes.
However, it has been impossible to apply the method of inserting the special reproduction information into AV data to real-time recording of data into recording mediums such as DVD-RAMS.
This is because in real-time recording of AV data, information on a part of the AV data to be recorded from now on (e.g., addresses of NV packs in the backward direction) cannot be obtained.
Also, it is possible to generate special reproduction information to be recorded in each NV pack after the AV data is recorded. However, to record the generated information into an AV data storage area as NV packs, the same number of accesses to the disc as the number of VOBUs are required. This cannot be achieved in real time.
Some may think that this problem will be solved by storing the AV data and the special reproduction information in different AV data areas. However, this solution has another problem that to store the special reproduction information in a main memory, the main memory should have a large capacity, where the storage of the special reproduction information in the main memory is necessary to execute the special reproductions at high speed.